1. Field of the Invention
The present invention relates to a process for producing a multilayer molded article having a skin material laminated with at least a part of the surface of a substrate formed of a thermoplastic resin, etc.
2. Description of the Related Art
Multilayer molded articles in which a skin material having a foamed layer is laminated in one piece to the surface of a substrate formed of a thermoplastic resin have been widely used in many fields such as interior parts of automobiles (for example, door trims and instrument panels), interior and exterior parts of household appliances, and the like.
Hitherto, as a manufacturing process of such multilayer molded articles have been known, for example, a process comprising laminating and adhering a skin material, by using adhesive or the like, to a substrate produced in advance by variety of methods such as injection molding and compression molding and a process comprising supplying a skin material to between a pair of mold halves and thereafter supplying a molten thermoplastic resin, thereby giving a desired shape to the molten resin to form a substrate and simultaneously laminating the skin material in one piece to the surface of the substrate.
However, among such processes, the former process has complex steps and also has problems on the human body, the environment and the like caused by a solvent contained in the adhesive. The latter process has an advantage of being capable of forming a substrate and simultaneously laminating a skin material onto the surface of the substrate, but also has a problem that when a molten thermoplastic resin of high temperature and high pressure is supplied into a mold, the high pressure molten resin comes in contact with a skin material and the skin material is pressed against a molding surface, and as a result, feeling of the resulting skin material is damaged. In particular, there has been a problem that when a skin material having a foamed layer is used, the foamed layer is crushed and cushion property is deteriorated.
In particular, in the case of a skin material having a foamed urethane layer as a foamed layer, the foamed layer is noticeably crushed. A known measure against this problem is to back the foamed layer. However, no attention heretofore has been directed to a relationship between the density of the foamed urethane layer and the weight of the backing layer at all, and the backing layer has been made as thin as possible. There therefore has been a problem that the foamed layer can not be fully protected.
Under these circumstances, in order to produce a multilayer molded article at low cost with taking advantage of the benefit of injection molding, compression molding or the like of being capable of forming a substrate and simultaneously laminating a skin material onto the surface of the substrate, even in the case of using a skin material having a foamed urethane layer, without impairment of the cushion property caused by crush of the foamed layer, the present inventors have found that a relationship between the density xcfx81 of the foamed urethane layer and the weight W of a backing layer is very important. As a result, they have accomplished the present invention.
That is, the present invention provides:
a process for producing a multilayer molded article having a skin material laminated with at least a part of the surface of a substrate formed of a thermoplastic resin, the process comprising supplying a skin material to between a pair of mold halves and supplying a molten thermoplastic resin to between the skin material and the molding surface of one of the mold halves, the process being characterized by using, as the skin material, a skin material which has at least a foamed urethane layer and a nonfoamed backing layer wherein the product of the density, xcfx81 (g/cm3), of the foamed urethane layer and the weight, W (g/m2), of the backing layer is not less than 2; and
a method for controlling crush of a foamed urethane layer in a multilayer molded article having a skin material with the foamed urethane layer, the skin material being laminated with at least a part of the surface of a substrate formed of a thermoplastic resin, the method being characterized by laminating such a backing layer that the product of the density, xcfx81 (g/cm3), of the foamed urethane layer and the weight, W (g/m2), of the backing layer is not less than 2 to the foamed urethane layer.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, and variations such as xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step.